Exit regex matching on unclosed MFM tag

lib/index.umd.js

@@ -94,6 +94,10 @@
         var walk = 0;
 
         while (level > 0 || walk === 0) {
+          if (walk >= src.length) {
+            return null;
+          }
+
           if (src[walk] + src[walk + 1] === '$[') {
             level++;
             walk++;

package.json

@@ -1,6 +1,6 @@
 {
   "name": "marked-mfm",
-  "version": "0.3.1",
+  "version": "0.3.2",
   "description": "Marked.js extension for Misskey-flavored Markdown",
   "main": "./src/index.js",
   "browser": "./lib/index.umd.js",

src/index.js

@@ -10,6 +10,9 @@ export default {
         let level = 0
         let walk = 0
         while (level > 0 || walk === 0) {
+          if (walk >= src.length) {
+            return null
+          }
           if (src[walk] + src[walk + 1] === '$[') {
             level++
             walk++